Ovulation & Due Date Calculator
Ovulation & Due Date Calculator estimates your fertile window, ovulation date and potential due date from your last period date and average cycle length.
Last updated: July 2026
An ovulation calculator estimates when you ovulate and your fertile window based on your last period and cycle length. A typical 28-day cycle ovulates around day 14.
🔒 All calculations run in your browser. Based on average cycle data — not a substitute for medical advice.
How to use Ovulation & Due Date Calculator
- Enter the first day of your last period.
- Enter your average cycle length (default 28 days).
- Read your estimated fertile window, ovulation date and due date.
Frequently asked questions
How accurate is this?
It provides estimates based on averages. Individual cycles vary — use it as a guide.
What if my cycle is irregular?
The calculator works best with regular cycles (21–35 days).
Is my data stored?
No — all calculations run in your browser.
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